Fixed bed, fluidised bed or stirred tank reactors are conventionally used for the synthesis of hydrocarbons from starting materials including carbon monoxide, carbon dioxide and/or hydrogen. The efficiency of existing fixed bed, fluidised bed and stirred tank reactors is limited by amongst other factors, mass transfer limitations and the creation of hot spots within the bed of catalyst.
Hot spots in a fixed catalyst bed promote conversion of carbon monoxide and/or carbon dioxide and hydrogen to methane, thereby reducing conversion to heavier hydrocarbons. Hot spots also cause catalyst deactivation.
Mass transfer limitations within catalysts in a fluidised bed or stirred tank reactor, reduce the effective rate of reaction and therefore rate of alcohol and aliphatic hydrocarbon production.
One means by which the mass transfer limitations can be reduced is by the means of a structured monolithic catalyst. U.S. Pat. No. 6,262,131 teaches that structured catalyst can have benefits in terms of activity and heat transfer for the conversion of gases to hydrocarbons but demonstrates that conventional structured catalyst typically has little effect on the selectivity of the reaction.
WO 98/38147 also describes how structured channel catalysts can be used to produce solely hydrocarbons by use of cobalt-containing catalysts.
It is known that higher alcohols can be produced by the use of cobalt catalyst co-precipitated with other metals, principally copper. Further, alkalisation increases the selectivity to alcohols (Today 65 (2001) 209-216, Arislete Dantas de Aquino, Antonio José Gomez Cobo). However elevated pressure is required to see any significant production of alcohols.
Conventional wisdom informs that cobalt on alumina produces a catalyst for the production of hydrocarbons. Thus, for example J. CHEM. SOC., CHEM. COMMUN., 1985 1179 “Selective Production of Alkenes and Alcohols on Cobalt Catalysts in the Liquid Phase”, Michel Simon, André Mortreux, Francis Petit, Dominique Vanhove and Michel Blanchard, demonstrates that production of oxygenates does not exceed 10% under a wide range of conditions.
Furthermore, Applied Catalysis A: General Volume 186, Issues 1-2, 4 October. 1999, Pages 189-200, Martin Kraum and Manfred Baerns teaches that the effect of titania modification of the support is an increase in the dispersion of the catalyst and does not give an oxygenate-producing catalyst with cobalt.
At pressures as low as 10 bar, commercial practice for production of fuels in the 1940s, 90% selectivity to hydrocarbons was found.
Production of higher alcohols is known via the OXO process where high pressure hydroformylation is catalysed by homogeneous cobalt catalysts. However, this requires an alkenic feedstock as well as carbon monoxide and hydrogen.